Systems and methods for the detection and analysis of free thiol

Embodiments described herein relate to devices, and methods for quantifying thiol content in a sample containing a mixture of proteins or protein isoforms. The method includes conjugating a portion of the sample with free thiol detection binders, separating the contents in the portion of the sample into separated protein isoforms, detecting fluorescence signals associated with each separated protein isoform, and quantifying, based on the fluorescence signals, a relative amount of free thiol associated with each separated protein isoform. In some instances, the method includes quantifying the amount of each separated protein isoform based on absorbance signals associated with each separated protein isoform. In some instances, the fluorescence and/or absorbance signals associated with protein isoforms conjugated with detection binders can be compared with the corresponding signals associated with unconjugated protein isoforms. In some instances, the method further includes applying a reducing agent and quantifying total-thiol content in the sample.